Process for extracting solvent from polyamide filaments

ABSTRACT

A PROCESS FOR EXTRACTING SPIN-MIX SOLVENT FROM A MOVING CONTINUOUS BUNDLE OF DRY-SPUN SYNTHETIC FILAMENTS AND FOR DETECTING DRIPS ALONG THE FILAMENT BUNDLE. THE PROCESS COMPRISES SEQUENTIALLY (1) PASSING THE BUNDLE IN A SUBSTANTIALLY STRAIGHT PATH BETWEEN A PAIR OF RIGID CORRUGATED SHEETS POSITIONED IN PARALLEL PLANES SUCH THAT THEY COOPERATE TO FORM AN UNDULATING CHANNEL BETWEEN THEM, (2) FORCING A LIQUID, WHICH IS A SOLVENT FOR THE SPIN-MIX SOLVENT BUT NOT FOR THE POLYMER OF WHICH THE SYNTHETIC FILAMENTS ARE COMPOSED, THROUGH THE UNDULATING CHANNEL AT A VELOCITY WHICH CAUSE IT TO PASS ALONG THE CHANNEL BACK AND FORTH THROUGH THE BUNDLE, AND (3) PASSING THE FILAMENTS PASS AN APPENDAGE THAT IS ADJUSTABLE TO ALLOW PASSAGE OF A STANDARD THICKNESS CONTINUOUSLY MOVING BUNDLE BUT TO PREVENT PASSAGE OF A BUNDLE OF LARGER THAN STANDARD THICKNESS. THE APPENDAGE CONTAINS PASSAGEWAYS THROUGH IT TO PERMIT CARRY-OFF OF SAID LIQUID.   D R A W I N G

May 1, 1973 c BOWEN ET AL 3,730,680

PROCESS FOR EX'IRAC'I'ING SOLVENT I ROM'POIJYAMHH'I FILAMENIS FIG.2

Filed Jan. 5, 1972 FIG- United States Patent Oflice 3,730,680 Patented May 1, 1973 3,730,680 PROCESS FOR EXTRACTING SOLVENT FROM POLYAMIDE FILAMENTS Braxton C. Bowen and Jackie A. Weir, Richmond, Va., as-

signors to E. I. du Pont de Nemours-and Company,

Wilmington, Del.

Filed Jan. 5, 1972, Ser. No. 215,603 Int. Cl. D06c 1/06 US. Cl. 8'-151.2 3 Claims ABSTRACT OF THE DISCLOSURE A process for extracting spin-mix solvent from a moving continuous bundle of dry-spun synthetic filaments and for detecting drips along the filament bundle. The process comprises sequentially (1) passing the bundle in a substantially straight path between a pair of rigid corrugated sheets positioned in parallel planes such that they cooperate to form an undulating channel between them; (2) forcing a liquid, which is a solvent for the spin-mix solvent but not for the polymer of which the synthetic filaments are composed, through the undulating channel at a velocity which causes it to pass along the channel back and forth through the bundle; and (3) passing the filaments past an appendage that is adjustable to allow passage of a standard thickness continuously moving bundle but to prevent passage of a bundle of larger than standard thickness. The appendage contains passageways through it to permit carry-off of said liquid.

BACKGROUND OF THE INVENTION (1) Field of the invention This invention is concerned with a process for the production of synthetic filaments by dry spinning. More particularly, the invention is directed to a process for more efficient extraction of solvent from synthetic dry-spun filaments and for the detection of certain yarn defects.

(2) Description of the prior art In most dry-spinning processes for spinning filaments from a polymer, the solvent used in the spin mix is removed from the spun filament by dry heat followed by extraction. The use of dry heat rapidly evaporates most of the solvent, thus promoting gelation of the filaments. Residual solvent is usually removed by extraction with a liquid in which the solvent is soluble and the polymer insoluble. One type of apparatus in use for extraction of spun filaments is described in US. Pat. No. 3,493,422, while another is described in US. Pat. No. 3,343,383. It would be desirable to provide an extraction procedure with good efficiency; for the more efficient the extraction, the less extractant needed for use in the process. The present invention provides an efiicient extraction procedure.

In addition, in dry spinning processes, particularly in the spinning of aromatic polyamides, drips of solution sometimes form on the filaments as they emerge from the spinneret. These drips are lumps of partly hardened solution produced when a spinneret opening fails to jet its spinning solution perpendicularly away from the face of the spinneret. In such an instance the the solution collects on the face of the spinneret and then forms a drip on the emerging filaments. The presence of these drips is detrimental because they render the filaments nonuniform in diameter and alter other physical properties, such as strength, at the point of the drip. It is important that drips which do occur be detected early. The present invention provides for the early detection of such drips by combining the efiicient extraction procedure (which extracts solvent thus allowing the polymer remaining in SUMMARY OF THE INVENTION This invention provides a process for extracting spinrnix solvent from a moving continuous bundle of dryspun synthetic filaments and for detecting drips along the filaments, which comprises in sequence:

(1) passing the bundle, preferably freshly spun, in a substantially straight path between a pair of rigid sheets, each having a series of parallel, equally spaced curved ridges and hollows, said sheets being positioned in parallel planes such that the curved ridges and hollows cooperate to form an undulating channel and being spaced apart at a distance which causes liquid entered between the sheets to pass along the undulating channel back and forth through the bundle of filaments;

(2) forcing a liquid, which is: a solvent for the spinmix solvent but not for the polymer of which the synthetic filaments are composed, through the undulating channel at a velocity which causes it to pass along the channel back and forth through the bundle; and

(3) passing the filaments past an adjustable appendage located downstream from the point the liquid is entered into the undulating channel, said appendage being adjustable to allow passage of a standard thickness continuously moving filament past it, but to prevent passage of a larger than standard thickness filament, said appendage having passageways through it constructed to permit passage and carry-off of said liquid.

DESCRIPTION OF THE DRAWINGS The process may be more easily understood by reference to the drawings in which FIG. 1 is a cross-sectional view of the rigid sheets which form the undulating channel;

FIG. 2 is an elevation view of the sheet on the right side of FIG. 1; and

FIG. 3 is an enlarged view of part 19 of FIG. 1.

DESCRIPTION OF THE INVENTION In the figures, a bundle or sheet of spun synthetic filaments 10 (preferably freshly spun and preferably an aromatic polyamide, i.e., one whose -NHCO-- linkages are directly attached to a carbon atom of an aromatic ring, such as poly(metaphenylene isophthalamide) is conducted into casing 11 through entrance port 13. Preferably, casing 11 is positioned to allow the filaments 10 to be conducted vertically through the casing. Extracting liquid is admitted through inlet ports 14 and 15. When the filaments are made from an aromatic polyamide the liquid will preferably be water. Casing. inserts 16 and 17 carry the curved ridges and hollows 18 which form a corrugated interior surface. By matching the corrugations an undulating path through the casing is provided. As shown in FIG. 2, except for the corrugations, the interior surface of the inserts is fiat. By means of adjustments not shown the width between opposing ridges and hollows of inserts 16 and 17 can be varied to confine the filaments lightly and to inhibit flow of liquid in a path parallel to the filament path. Thus, the liquid is forced to follow the undulating channel and consequently makes a plurality of passes through the filaments, resulting in efficient extraction of solvent and impurities from the filament strands.

Adjustable appendage 19 is adjusted relative to opposing apex 20 of insert 16 to allow filaments of normal thickness to pass through the resulting passageway, but not filaments carrying a drip (which filaments will have a bulge of semi-hardened polymer at the point of the drip). A passageway or opening 21 in appendage 19 allows the extractant liquid to pass through to outlet 22.

This opening is necessary to prevent back-flooding which would otherwise occur when a drip-containing portion of the filaments plugs up the passageway between appendage 19 and apex 20. Upon plugging by the drip the movement of the filaments through the casing will cause them to snap, thus alerting an operator to the existence of a defective portion of filaments.

The advantage of the process of this invention over the process of Berry U.S. Pat. No. 3,493,422 is shown by the following comparison experiment. The Berry patent equipment used was similar to that depicted in FIG. 3 of the Berry patent. In the comparison an aromatic polyamide of the type described in the Kwolek et al. US. Pat. No. 3,063,966, specifically poly(metaphenylene isophthalamide), was spun from a solution in dimethyl acetamide (DMAc) containing calcium chloride to obtain a 2800- filament, 9.6 denier-per-filament yarn (as-spun basis), and was wound up at a rate of 180 yards per minute. As the filaments emerged from the spinning enclosure, they contained approximately -30% CaCl and 80-100% DMAc (based on polymer, before quenching). In each instance, the filaments were continuously conducted to the extraction apparatus immediately upon emergence from the heated spinning enclosure. There, they were flooded with solutions containing the amounts of solvent and salt indicated in Table 1. In each case, the liquid efiluent issuing from the extraction apparatus was analyzed to establish the change in its composition, and from these data, a calculation was made to determine the amount of solvent and salt removed from the filament yarn per hour. Flooding liquid was used at a rate of 8 or 9.5 lbs/lb. of filament yarn in each case in the process of this invention but a larger amount of liquid was used in the process of the Berry patent. Results are as follows:

obvious modifications will occur to those skilledinthe art.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

5 *1. A process [for extracting spin-mix solvent from a moving continuous bundle of dry-spun synthetic filaments and for detecting drips along the filaments, which comprises in sequence '1. A process for extracting spin mix solvent from a between a pair of rigid sheets, each having a series of parallel, equally spaced curved ridges and hollows, said sheets being positioned in parallel planes such that the curved ridges and hollows cooperate to form an undulating channel and being spaced apart at a distance which causes liquid entered between the sheets to pass along the undulating channel back and forth through the bundle of filaments;

(2) forcing a liquid, which is a solvent for the spinmix solvent but not for the polymer of which the synthetic filaments are composed, through the un-' dulating channel at a velocity which causes it to pass along the channel back and forth through the bundle;

(3) passing the filaments past an adjustable appendage located downstream from the point the liquid is entered into the undulating channel, said appendage being adjustable to allow passage of a standard thickness continuously moving filament past it, but to prevent passage of a larger than standard thickness filament, said appendage having passageways through it constructed to permit passage and carry-off of said liquid.

2. The process of claim 1 wherein the pair of ridged sheets are arranged so that the bundle will pass vertically between them.

TABLE 1 Concentrations of flooding liquor Feed Eflfluent Water composition, composition, (1b rfige percent percent Material removed, lbs.

Process filament) DMAc CaClz DMAc CaCl; DMAc/hr. CaClz/hr.

Invention 8 6. 5 1. 89 8. 8 2. 99 1.92 J2 Invention 8 5. 4 1. 51 8. 5 3. 26 2. 59 1. 46

Invention 9. 5 4. 8 1. 76 6. 5 2. 2 3.1 90

Invention'l' 8 0.9 0.19 3. 0 1.33 5. 2 2. 6

It is seen that improved efficiency of extraction is real ized with the process of this invention over that of the Berry patent. The significance of this improvement is seen not only in economy of flooding liquor and reduced me chanical damage in handling of the filaments through packaging the subsequent extraction steps, but also in the positive detection and elimination of drips which if al lowed to remain with the filamentary product would seriously restrict its utility.

It has been found that in the absence of appendage 19, adjustment of inserts 16 and 17 to a clearance close enough to damage the filaments will not result in detection of drips, because the drips appear to deform sufiiciently to pass through a slot thinner than their normal thickness. However, when the appendage is employed and placed downstream from the extraction step, the more efficient extraction provided by the process of this invention results in the stiffening of the drips to cause them to be trapped in every case. When this occurs, all filamerits produced in that enclosure are broken back, and the absence of production therefrom serves as an indication that the spinneret needs servicing.

The foregoing detailed description has been given for clearness of understanding only and no unnecessary limitations are to be understood therefrom. The invention is 3. The process of claim 2 wherein the liquid comprises water and the polymer from which the filaments are made is an aromatic polyamide.

References Cited US. Cl. X.R.

not'limited to the exact details shown and described for 

